There's a lady on FB who has used 4 feeder goldfish to cycle a 29g tank. She's selling a 10 gallon and is giving away the gold fish. I've been told they're healthy with no problems. I was going to keep them in my hospital tank, but I haven't had a chance to switch everyone around yet and divide my 10g for newbie. Which leads to my question. Assuming they are all healthy, I'm going to her house to pick them up tomorrow so I will see their set up, etc, can they go in with Cooper for a few days until I can get everything to divide my tank? Coop is in a 5 gallon, so I'm fine with having to do extra water changes if needed. His tank doesn't have a heater but the water temp stays between 74-76 degrees since it's in my room. I've had goldfish in a community, but I've never kept one with my betta. The one and only time I had a male betta in a community, he killed everything but my dwarf frog. She said these are maybe half to an inch long, so they should be fine in my 5 gallon for now. Opinions? Thoughts? I figure I can always rehome these later if needed, but would give Cooper a possible distraction from his tail biting (which has become habit now). She said she had photos of them on her FB page but her pics are private. So I haven't been able to see for myself anything yet.

ETA: Hospital tank is a 1 gallon so it's pretty much out of the question for now. Newbie is in it, but only due to treating him for splitting his tail fin. *my fish are sillies* But 1 gallon would be WAY too small for 4 feeders anyway, so I'm left with either kicking Coop out of his 5 and putting him in a 1 gallon bowl (which he hates) or trying to assimilate the 5 together for a few days.

Not a good idea. Period.
I had 2 goldfish about the same size as yours along with 4 rosy barbs earlier this year, *my boyfriend won them for me at the fair* and I had to do water changes Every DAY!
thats in a 10 gallon! I know the barbs bio load isnt that high so those 4 and 2 goldfish is probably equivalent to your 4 goldfish. if you put them into a 5 gallon, that's going to be atleast 2x daily.
And re-homing goldfish is a very hard thing to do if you want them to go to experienced fish keepers

You can keep goldfish and betta tougher as long as you keep up with water quality - goldfish are very messy and poop constantly; and the temperature in upper 70ties. Despite the common belief fancy goldfish do well in warm water and are healthier.
I have betta with 4 goldfish and some guppies in 30 gal tank for 3 years now. I keep temperature around 74-76 and water immaculate clean - 30% water change every week with additional bottom syphoning and filter flushing 5x per week.
I got separate tank and moved him while ago but he got depressed - didn't eat for 4 weeks till I moved him back. He has his planted corner loves to stay in and delicious fresh guppy babies once in a while.

get a decent size rubbermaid container. these fish have drastically different needs and should not be forced to cohabitate with eachother. goldfish are cold water fish.the warmest they can handle without aging prematurely is around 70. they also put off alot of waste from their respiration alone, much less their defecation. feeder goldies can still get enormous. if you plan to keep these goldies and let them live up to their potential, you're gonna need a 60 gallon coldw ater tank with 2-3x filtration.

I say keep the hospital tank for the betta and then keep the goldfish in a larger tank. Goldfish like company and can get very large.
Betta do better in warm water while goldfish in cold water.
Goldfish produce more waste and will take over the tank quickly.